This invention relates generally to imaging and, more particularly, to prescribing scan parameters for scans in a multislice imaging system.
In at least some medical imaging systems generally known as computed tomograph (CT) imaging systems, an x-ray source projects a fan-shaped beam which is collimated to lie within an X-Y plane of a Cartesian coordinate system and generally referred to as the "imaging plane". The x-ray beam passes through the object being imaged, such as a patient. The beam, after being attenuated by the object, impinges upon an array of radiation detectors. The intensity of the attenuated beam radiation received at the detector array is dependent upon the attenuation of the x-ray beam by the object. Each detector element of the array produces a separate electrical signal that is a measurement of the beam attenuation at the detector location. The attenuation measurements from all the detectors are acquired separately to produce a transmission profile.
In known third generation CT systems, the x-ray source and the detector array are rotated with a gantry within the imaging plane and around the object to be imaged so that the angle at which the x-ray beam intersects the object constantly changes. X-ray sources typically include x-ray tubes, which emit the x-ray beam at a focal spot. X-ray detectors typically include a post patient collimator for collimating scattered x-ray beams received it the detector. A scintillator is located adjacent the post patient collimator, and photo diodes are positioned adjacent the scintillator.
Multislice CT systems are used to obtain data for an increased number of slices during a scan. Known multislice systems typically include detectors generally known as 3-D detectors. With such 3-D detectors, a plurality of two rows of detector elements, and a four slice detector has four rows of detector elements. During a multislice scan, multiple rows of detector cells are simultaneously impinged by the x-ray beam, and therefore data for several slices is obtained.
In single slice systems, a feature generally referred to as graphic Rx (prescription) is utilized to assist a user in prescribing axial, helical or cine scans by showing "cut" lines" superimposed on one or more scout images. The "cut" lines describe the image location, image interval, image display field of view (DFOV), image center in the X/Y plane, and image tilt. The graphic Rx controls are provided through a bidirectional interface with a text based graphical user interface (GUI) so that changes to key scan parameters made in one mode (e.g., the graphic Rx mode) are automatically updated in the other (e.g., text based GUI mode).
For single slice scanning display, and in the graphic Rx mode, the image center locations which correspond to the scan center locations and the laser light position are displayed. This relationship simplifies translations from scan and reconstruction parameters. For example, the following relationship exists in single slice scanning: EQU laser light position=scan plane location=image plane location
In multislice scanning, however, and since there is only one scan plane but multiple detector rows, the following relationship exists: EQU laser light position=scan plane location (not=) image plane location.
In addition, graphic Rx is impacted by the ability of the user to select various image thickness options, and the number of images per gantry rotation, as reconstruction parameters. Also, the ISO centers of tilted scans are offset up/down due to the detector rows physically being offset above and below the true ISO center. This offset is corrected algorithmically, impacting the image ISO center and maximum field of view.
In spite of the differences between single slice and multislice image display, it would be desirable to provide a graphic Rx mode in a multislice imaging system to assist a user in prescribing axial, helical or cine scans.